The present invention relates to a method of manufacturing a recording medium in which very small concavities and convexities such as pits comprising recording marks or grooves are formed, a method of manufacturing a recording medium manufacturing master, an apparatus for manufacturing a recording medium and an apparatus for manufacturing a recording medium manufacturing master, for example.
The above-mentioned master is a stamper itself for molding a recording medium having very small concavities and convexities formed thereon by injection molding or 2P method (Photopolymerization method), a master for manufacturing a so-called master used to transfer and duplicate a plurality of stampers and a master such as a so-called mother master used to transfer and duplicate a plurality of masters, for example.
In recent years, there is an increasing demand for increasing a recording density.
In recent years, in an optical pickup for reproducing a recording medium, there is proposed a so-called near-field arrangement in which a distance between a recording medium and an optical lens is selected to be under 200 nm. According to this arrangement, an N. A (numerical aperture) of an optical lens system can be increased and a diameter of a beam spot can be reduced by using reproducing laser light having a short wavelength, i.e., violet laser light, whereby a track pitch can be reduced and a width and a length of a recording mark can be reduced. Thus, a recording density can be improved more.
A diameter of a beam spot of reproducing light is generally selected to be about twice the width of the recording mark in order that the recording mark can be read out from the optical disk with a high reliability. In other words, the recording mark formed on the recording medium should preferably be selected to be under xc2xd of a diameter of a minimum beam spot that can be formed by reproducing light.
Currently, in the manufacturing process of the recording medium, e.g., in the manufacturing process of the master, for example, in general, as shown in a schematic cross-sectional view of FIG. 8, a photosensitive material layer 102 is formed on a substrate 101 comprising a master, e.g., glass substrate by spin coating. Laser light 103 is focused on this photosensitive material layer 102 by a condenser lens 104 and irradiated on the photosensitive material layer in response to desired data that should be recorded, for example. Thereafter, when this photosensitive material layer 102 is developed, the patterning of the photosensitive material layer 102 is effected by removing the area which had been reacted in photosensitivity with irradiation of laser light, for example. Then, very small concavities and convexities corresponding to recording data are formed by etching the substrate 101 while this photosensitive material layer is being used as a mask.
As shown by an example of a xcex3 (gamma) curve in FIG. 9, a characteristic of a photosensitive material has a characteristic which is exposed and reacted rapidly, i.e., which is exposed and reacted substantially stepwise in a light exposure greater than a certain light exposure. Therefore, when the photosensitive material is exposed by laser light having a laser light power distribution of a curve 202, in FIG. 10B, having power larger than this power as compared with a case in which this photosensitive material is exposed by laser light having a laser light power distribution shown by a curve 202 shown in FIG. 10A, a substantial photosensitive reaction area in the photosensitive material layer 102 is widened to a certain extent but this widened photosensitive reaction area does not lead to the area corresponding to exposure power.
Accordingly, in the above process for manufacturing the recording medium manufacturing matter, when the photosensitive material layer is exposed with a luminous pattern shown by a curve 203 in FIG. 11A, for example, while laser light spirally scans the photosensitive material layer with rotation of the above substrate 101, for example, as shown in FIG. 11B, an exposed portion 102A corresponding to a laser light irradiation pattern is formed on the photosensitive material layer 102 deposited on the substrate 101. Then, very small convexities and concavities formed after this exposed portion, for example, had been removed by development and the substrate 101 had been etched by using this photosensitive material layer 102 as an etching mask are formed as stable patterns as shown by a plan view of concave portions 103 formed as recording marks, for example, in FIG. 11C.
However, in this case, the very small concavities and convexities formed by pattern-exposing this photosensitive material layer are substantially determined by a diameter of a spot of laser light for use in exposure so that very small convexities and concavities which are over an optical limit cannot be formed. Accordingly, even when a diameter of a beam spot of reproducing laser light, for example, is reduced as much as possible, a width of recording mark cannot be reduced under xc2xd of the diameter of the beam spot of this reproducing laser light.
Although an electron beam writing apparatus and the like are developed as a pattern exposure apparatus for photosensitive material layers as an aide to form very small patterns and to increase a density, this electron beam writing apparatus has to execute writing in the high vacuum atmosphere. There then arises a problem that this apparatus becomes large in size and expensive.
It is an object of the present invention to provide a method of manufacturing a recording medium and a method of manufacturing a recording medium manufacturing master in which very small concavities and convexities having widths or track pitches sufficiently smaller than a beam spot of an optical limit of laser light used to form very small concavities and convexities can be formed independently of lengths of very small concavities and convexities.
Further, it is another object of the present invention to provide an apparatus for manufacturing a recording medium and an apparatus for manufacturing a recording medium manufacturing master having simple structures and which can be constructed as sufficiently small apparatus as compared with the above electron beam writing apparatus.
In a method of manufacturing a recording medium having very small concavities and convexities, a recording medium manufacturing method according to the present invention is comprised of a process for forming a thermosensitive material layer on a substrate comprising a recording medium, a process for forming a denatured portion with patterns corresponding to target very small concavities and convexities on the thermosensitive material layer by irradiating laser light on this thermosensitive material layer with patterns corresponding to the target very small concavities and convexities and a process for patterning this thermosensitive material layer by developing this thermosensitive material layer. Then, in particular, according to the present invention, pattern irradiation of laser light is executed by irradiation of laser light modulated by a frequency higher than a period of the target very small concave and convex patterns.
A method of manufacturing a recording medium manufacturing master according to the present invention is a method of manufacturing a recording medium manufacturing master for manufacturing a recording medium having very small concavities and convexities. This method is comprised of a process for forming a thermosensitive material layer on a substrate comprising a recording medium, a process for forming a denatured portion with patterns corresponding to very small concavities and convexities on the thermosensitive material layer by irradiating laser light on this thermosensitive material layer with patterns corresponding to very small concave and convex patterns and a process for patterning the thermosensitive material layer by developing the thermosensitive material layer. Then, in particular, according to the present invention, pattern irradiation of laser light is executed by irradiation of laser light modulated by a frequency higher than a period of target very small concave and convex patterns.
A recording medium manufacturing apparatus according to the present invention is an apparatus for manufacturing a recording medium having very small concavities and convexities and is comprised of a holding means for holding a substrate comprising a recording medium in which a thermosensitive material layer is deposited at least on one major surface, a laser light source section, a modulating means for modulating laser light from this laser light source section in response to patterns of very small concavities and convexities and which modulates laser light by a frequency higher than a period of patterns of very small concavities and convexities, an optical system including a condenser lens system for focusing laser light on the thermosensitive material layer and a moving means for moving the irradiation position of laser light relative to the thermosensitive material layer.
Further, an apparatus for manufacturing a recording, medium manufacturing a maser according to the present invention is an apparatus for manufacturing a recording medium having very small concavities and convexities and is comprised of a holding means for holding a substrate comprising a master in which a thermosensitive material layer is deposited at least on one major surface, a laser light source section, a modulating means for modulating laser light from this laser light source section in response to patterns of very small concavities and convexities and which modulates laser light by a frequency higher than a period of the patterns of the very small concavities and convexities, an optical system including a condenser lens system for focusing laser light on the thermosensitive material layer and a moving means for moving an irradiation of laser light relative to the thermosensitive material layer.
As described above, in the recording medium and the method of manufacturing the medium manufacturing master according to the present invention, unlike the conventional ordinary photosensitive material layer, the thermosensitive material layer is used and a thermally-denatured portion is formed on the thermosensitive material layer by irradiating laser light on the thermosensitive material layer. Then, this denatured portion or the portion other than this denatured portion is removed by development and the denatured portion is formed on a heated region whose width is narrower than the beam spot of the laser light by patterning. That is, there can be formed very small patterns which are under the optical limit of the beam spot of the laser light.
Further, in the recording medium and the method of manufacturing the medium manufacturing master according to the present invention, in particular, laser light which was modulated to have a frequency higher than a period of the very small concavities and convexities is irradiated. With this arrangement, the heated portion which is generated with continuous irradiation of laser light based on the length of the exposure portion, i.e., a duration of an exposure time can be prevented from being widened and the denatured portion of the accurate predetermined shape, the width and the pitch can be formed. Thus, it becomes possible to accurately form target very small patterns.
Furthermore, in the recording medium and the apparatus for manufacturing the medium manufacturing master, since processing work within the high vacuum chamber is not required, a simple and small apparatus can be constructed.